Liquid crystal optical processor

ABSTRACT

The optical processor employs a photoconductor-activated liquid crystal as a spatial filter to control transmissivity of coherent light through the processor. The liquid crystal filter pattern determines the pattern input to Fourier transform and can optionally also define the transmissivity of a Fourier processing filter. This permits near real time transform.

United States Patent 1 Beard et al.

[4 1 July 10, 1973 LIQUID CRYSTAL OPTICAL PROCESSOR Inventors: Terry D.Beard, Woodland Hills;

' William P. Bleha, Jr., Santa Monica,

both of Calif.

Hughes Aircraft Company, Culver City, Calif.

Filed: Oct. 26, 1971 Appl. No.1 192,406

Assignee:

US. Cl. 350/162 SF, 350/35, 350/160 LC Int. Cl G021) 27/38, G06q 9/00Field of Search 350/3.5, 162 SF,

1 References Cited UNITED STATES PATENTS 6/1959 Baurnann et al 350/160LC 7/1971 Conners 350/160 LC 4/1963 Carlson 350/162 SF OTHERPUBLICATIONS Myers et al., IBM Technical Disclosure Bulletin, Vol.

11, No. 10, March 1969, pp. 1314-1316.

MacAnally, Applied Physics Letters, Vol. 18, No. 2, Jan. 1971, pp.54-56.

Margerum et al., Applied Physics Letters, Vol. 17, No. 2, July 1970, pp.51-53.

Primary Examiner-David Schonberg Assistant ExaminerRonald J. Stern vAttorney-W. H. MacAllister, Jr. and Allen A. Dicke,Jr.

[5 7 ABSTRACT The optical processor employs a photoconductoractivatedliquid crystal as a spatial filter to control transmissivity of coherentlight through the processor. The liquid crystal filter patterndetermines the pattern input to Fourier transform and can optionallyalso define the transmissivity of a Fourier processing filter. Thispermits near real time transform.

16 Claims, 3 Drawing Figures PATENIEUJUL 1 man 3. 744879 LIQUID CRYSTALOPTICAL PROCESSOR BACKGROUND This invention is directed to an opticalprocessor in the form of an optical computer which incorporates aphotoconductor-activated liquid crystal to control opticaltransmissivity.

The prior art includes knowledge that, through optical data processing,mathematical techniques can be employed in a manner similar to thoseemployed in electronic computations. It has been recognized that thetwo-dimensional capability of optical systems is such thattwo-dimensional signals such as pictures can be processed as a whole,without the necessary scanning, as in electronic systems. Holographictechniques add a third dimension to the data capable of being processed.The ultimate potential of optical computing or data processing systemshas not been reached. Working systems have been developed for theprocessing of information in the specialized area of seismography,radio-astronomy, and radar. Furthermore, optical systerns have thepotential capability of processing communication signals and othercomplex data signals.

Further background on the utility and some of the techniques of opticalprocessing are found in the book Optical Data Processing, by Arnold RoyShulrnan, Wiley, N.Y., 1970. Another publication in this field isFourier Optics, by Joseph Goodman, Stanford University Press. The entiredisclosures of these publications are incorporated herein by thisreference.

The data inserted in prior optical processes was in the form ofphotographic film. In preparation of this data, processing was very slowand inconvenient. Other methods considered for the introduction of inputdata have suffered from irreversibility, like photographic film, orsuffer from insensitivity, or inefficiency with coherent light. Thus,prior structures for the introduction of data as input to an opticalprocessor have been unsatisfactory.

SUMMARY In order to aid in the understanding of this invention, it canbe stated in essentially summary form that it is directed to a liquidcrystal optical processor. The optical processor includes an opticalaxis, along which the coherent light travels. Optical devices arepositioned along the axis to serve as input and output devices withrespect to the information contained in the light. One of the inputdevices comprises a photoconductoractivated dynamic scattering modeliquid crystal, for convenience in providing input information into thecollimated beam.

Accordingly, it is an object of this invention to provide a liquidcrystal optical processor which permits the introduction of informationinto the optical processor on a near real time basis. It is anotherobject to provide anoptical processor which incorporates a coherentlight path along an optical axis, with a dynamic scatterthe collimatedlight. It is a further object to provide a photoconductor'activateddynamic scattering mode liquid crystal device upon the coherent lightpath of an optical processor for efficiency in actuation. It is afurther object to provide a liquid crystal optical processor which has aliquid crystal at both the input plane and at a location adjacent thefocal point at the Fourier transform plane so that both the input datacontrolling ing mode liquid crystal on the path for the control of thecollimated light to the Fourier transform and the Fourier-processingfilter are liquid crystal devices.

Other objects and advantages of this invention will become apparent froma study of the following portion of the specification, the claims, andthe attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of anoptical processor incorporating a liquid crystal, in accordance withthis invention.

FIG. 2 is a schematic diagram of a liquid crystal as used in the opticalprocessor.

FIG. 3 is a further embodiment of a liquid crystal optical processor, inthis case also employing a liquid crystal adjacent the Fourier transformplane as a Fourier processing filter.

DESCRIPTION FIG. 2 illustrates a liquid crystal cell 10 which is aphotoconductor-activated dynamic scattering mode liquid crystal cellarrangement. The cell is a laminar structure. Glass substrate 12 isclear glass and is intended to be used for transmitting lighttherethrough. Therefore, it is preferably clear and flat with its outersurfaces substantially parallel. Quartz can also be employed as thestructure. Transparent, electricallyconductive coating 14 is applied toone side of the glass. One type of coating which is useful iscommercialy known as Nesa glass. This coating is specificallyantimony-doped tin oxide or tin-doped indium oxide. Instead of employingNesa glass, another convenient substantially transparent andelectrically conductive coating is taught by Alfred F. Kaspaul US. Pat.No. 3,698,946. A layer constructed in accordance therewith canalternatively be employed.'Another manner of forming the electrode layer14 can be by sputtering tin oxide or indium oxide onto the glasssubstrate 12. Furthermore, thin metal layers, such as gold, can beemployed for this purpose. The thickness of the transparent electricallyconductive coating should be such as to give a resistance inthe range offrom 10 to 1,000 ohms per square.

Photoconductor film 16 is deposited onto the coating 14 by conventionalvacuum deposition techniques. The photoconductors which are presentlyconsidered to be most desirable are zinc sulfide and cadmium sulfide.They can alternatively be used, or a layer of each is also useful.Thickness of the photoconductor film is from 0.5 to 12 microns.

On top of the photoconductive layer 16 is deposited a liquid crystallayer 20. The cell is completed by glass 22 on which is coatedtransparent conductive layer 24. The glass and its coating structurallycorrespond to glass 12 and its transparent conductive layer 14 describedabove. The two glass layers 12 and 22 thus define the outer surfaces ofcell 10.

Liquid crystals are known and there are publications directed to theirstructure and utility. There are three principal types of liquidcrystals of interest: nematic, cholesteric, and smectic. Several typesof electrical field-activated phenomena have been reported in nematicliquid crystals, or in nematic-cholesteric mixtures. A reversible lightscattering has been called dynamic scattering mode, and another mode isa phase mode in which the phase of the light passing through the liquidcrystal film is modulated. The phase modulation capabilities of liquidcrystal photoactivated light valves have also been used in this opticalcomputer. The principle of operation is that, when light falls on thephotoconductor film, its resistance is changed and thus the voltageappearing across the liquid crystal in contact with it is changed. Theindex of refraction of the liquid crystal depends on the voltage acrossit. Thus, the index of the film is modulated by the light falling on thephotoconductor. Coherent light pa ing through this film has its phasemodulated by this index difference in the liquid crystal film. Thus, thefilm acts as a photoactivated phase-modulating light valve and, as such,can be used as an optical processing input light valve.

There are two modes of liquid crystal activity employed in the opticalprocessor, in accordance with this invention. W hen a nematic liquidcrystal is sandwiched between two electrodes, such as electrodes 114iand 24, with proper spacing for liquid crystal thickness (the preferredliquid crystal film thickness is from 3 microns to 25 microns), anelectric field will affect the physical properties. The dynamicscattering mode is enhanced by employment of the photoconductive layer16. in the cell 10, when a voltage is applied to the electrodes, thehigh resistivity of the photoconductive layer, in the dark condition,prevents current from passing through the liquid crystal. However, whena spot on the photoconductive layer is optically activated, itsresistance is decreased and the voltage becomes applied to the liquidcrystal and produces an image in this area.

The photoconductor ZnS is ultraviolet-sensitive and is not sensitive tovisible light. The photoconductor CdS is sensitive in the blue and greenspectral regions and is not sensitive for wavelengths greater than 520nm. Thus, an image can be recorded or written on the liquid crystal cellmade with the photoconductor ZnS with ultraviolet light and viewed ordisplayed with visible light. With the photoconductor CdS, an image canbe recorded or written on the liquid crystal cell 10 with blue-greenlight and viewed or displayed-with light with wavelengths greater than520 nanometers. An exposure of only 0.1 millijoule cm can produce adynamic scattering mode image 50 milliseconds after exposure.

With the ultraviolet sensitivity of the ZnS photoconductive layer,illumination thereof with ultraviolet light, in the range of 300 to 400nanometers wavelength results in address of the liquid crystal. At thesame time, illumination of the cell for projection by transmission-typeprojection display in the visible wavelengths results in projecting theinformation that is on the liquid crystal device. When a helium-neonlaser is used as the projection illuminator as a source of collimatedlight, its wavelength is 632.8 nanometers, at which wavelength theliquid crystal is insensitive to address and exposure.

With the blue-green sensitivity of the CdS photoconductive layer,illumination thereof with blue-green light, ln-the range of 400 to 520nanometers wavelength results in an address of the liquid crystal. Atthe same time, illumination of the cell for projection bytransmission-type projection display for wavelengths greater than 520nanometers results in projecting the information that is on the liquidcrystal device. When a helium-neon laser is used as the projectionilluminator as a source of collimated light, its wavelength is 632.8nanometers, at which wavelength the liquid crystal cell is insensitiveto address and exposure.

it should be noted that other photoconductors than ZnS and CdS could beused for this device. The following table gives further examples ofseveral other photoconductors and their sensitivity wavelength range andprojection light wavelength range:

Sensitivity Range Projection Light Range (um) ZnO 300-390 400 CdSe400-730 730 Si 400-1220 1220 Ge 400-1970 1970 Thus, sensitivity foraddressing this liquid crystalphotoconductor device is possiblethroughout the visible and into the infrared. The projection light rangeis at wavelengths greater than the sensitivity range and thus, inseveral cases the use of coherent infrared light would be necessary forthe optical data processing. Other photoconductors having suitablecharacteristics could alternatively be used.

The nematic liquid crystal film is ordinarily transparent. However, whena current is passed through it, it becomes translucent and stronglyscatters light. This behavior occurs because the nematic liquid crystalmolecules are optically anistropic and, in the undisturbed state, theycooperatively align and behave optically like a uniaxial crystal film.However, when a current is passed through the film, the uniformstructure is disrupted, causing rapid spatial changes in the opticalindex and, as a consequence, light scattering.

As described above, the current is controlled by the photoconductor andthe addressing illumination thereof. The electric field is imposed byelectric contacts 26 and 28, which are respectively connected totransparent electrically conductive layers 24 and 1.4, respectively.When the crystal is nematic, a DC field is applied to attain thescattering effect. DC source 30 is serially connected with switch 32between the electrodes 26 and 28 to achieve the field application.Current density from 0.5 to 10 microamperes per square centimeter isrequired for strong scattering. This is achieved with application of 5to 50 volts DC. The power consumption is in the order of 0.1 microwattsper square centimeter.

0n the other hand, when a DC power supply in series with an AC supply isused to drive the liquid crystal cell, the background scattering of theliquid crystal in unactivated state is reduced. Furthermore, itdecreases the decay time of the photoactivated electric crystal. Thus,as an alternative source of electric field, AC source 38 is seriallyconnected with DC source 40 and through switch 42 to the two contacts 26and 28. Thus, when switch 42 is closed, a DC field with an ACsuperimposed bias is applied. The cells require from 1 to 10microamperes per square centimeter for activation and require an appliedvoltage from 5 to 50 volts DC with a superimposed AC bias of the samevalue as the DC, for example at 20 kilohertz. For a particular cell, theapplied voltage was 40 volts DC plus 27 volts RMS at 20 kilohertz.

The same nematic liquid crystal cell 10 can be used to provide phasemodulation as an input interface device for the optical processor.

The phase modulation capabilities of liquid crystal photoactivated lightvalves have also been used in this optical computer. The principle ofoperation is that,

when light falls on the photoconductor film, its resistivity is changedand thus the voltage appearing across the liquid crystal in contact withit is changed. The index of refraction of the liquid crystal depends onthe voltage across it. Thus, the index of the film is modulated by thelight falling on the photoconductor. Coherent light passing through thisfilm has its phase modulated by this index difference in the liquidcrystal film. Thus, the film acts as a photoactivated phase modulatinglight valve and, as such, can be used as an optical processing inputlight valve. In this case, the liquid crystal cell is operated with alower applied voltage, such as 1-10 volts. This voltage is below thatrequired to excite translucency or the dynamic scattering mode in theliquid crystal film. In this case, the liquid crystal film behaves likean electro-optic crystal with an extremely high electro-opticcoefficient so that, with an applied voltage of a few volts, efiicientphase modulation is possible. Again, the photoconductor 16 is used tospatially modulate the applied voltage by responding to the inputincoherent light image focused onto it.

In another application, the liquid crystal cell 10 employs anematic-cholesteric mixture. This mixture of liquid crystal media hasthe feature that it has the ability to store a light-scattered imageimpressed upon it. In the use of such a cell, an incoherent image isfocused onto the photoconductive film of the liquid crystal layer and aDC voltage is briefly applied. This is accomplished by brief closure ofthe switch 32 connected in series with DC source 30. A translucentlight-scattering reproduction of the addressed image will appear in theliquid crystal film and remain there, even after the DC voltage andincoherent image are removed. The cell is erased by briefly applying ahigh frequency across the cell. This is accomplished by AC source 34connected in series with switch 36 across the contacts 26 and 28.

Referring to F 1G. 1, the preferred embodiment of the liquid crystaloptical processor is generally indicated therein by the referencenumeral 50. This processor employs a laser 52 as the source of coherentlight. For

example, a helium-neon laser having a wavelength of 632.8 nanometers anda power of 18 milliwatts is useful as a specific source. The light fromthe laser is passed through a spatial filter 54 and is recollimated bylens 56.

From the recollimator lens 56, the light from the laser is passedthrough mechanical chopper 58. This chopper is an optional device andcomprises a rotating shutter structure having a 90 hertz choppingfrequency. The chopper is employed to allow accurate measurement at theprocessor output without the need for DC level correction. Next alongthe optical axis of processor 50 is liquid crystal cell 10. Aspreviously discussed, the liquid crystal cell 10 acts as a light valvewhich can be addressed so that portions thereof are transparent, whileother portions scatter transmitted light.

Address or exposure of the liquid crystal cell 10 is accomplished byproviding an image 60 which contains the information as to spatialcontrol of transparency of liquid crystal 10, as is desired. The image60 may be a back-illuminated transparency, or other image havingsufficient illumination to control the liquid crystal cell 10. The image60 is projected onto the cell 10 through shutter 62, lens 64, and beamsplitter 66. In this way, the image 60 is projected onto the liquidcrystal to control its light transmissivity, as previously described.The illumination of beam splitter 66 is ultraviolet. In the case of azinc sulfide photoconductor 16 in the cell 10, peak sensitivity is below400 nanometers and, with cadmium sulfide, peak sensitivity is below 520nanometers. Thus, ultraviolet for ZnS or blue-green for CdS illuminationat these wavelengths results in proper address of liquid crystal cell,while the laser beam at 632.8 nanometers does not affect the image onthe electric crystal. in the case of a nematic liquid crystal, theaddress is maintained, as long as spatial transparency controller liquidcrystal cell is desired. On the other hand, with the nematic cholostericmixture which has a memory, shutter 62 can be employed to address andimpress upon the cell the desired image. The liquid crystal is thus aspatial filter.

The coherent laser light is directed along the optical axis of thesystem. Spatial Fourier transform is produced by first transform lens68. It is placed one focal length down the optical axis from the liquidcrystal layer in the liquid crystal cell 10. Since the liquid crystalcauses scattering in the nontransparent areas, aperture plate 70 isplaced one focal length downstream from first Fourier transform lens 68.The aperture plate obstructs the scattered rays, but permits theunscattered rays from the transparent areas of the liquid crystal cellto pass through at the focus.

Downstream from aperture plate 70 and, thus, slightly below the focalpoint of lens 68, is the Fourier processing plane, at which filter 72 islocated. Filtration of the Fourier transform is accomplished at thisplane.

As is fully explained in the book Optical Data Processing, supra,filtration at the Fourier processing plane can be employed for removalof unwanted signals. Three focal lengths along the axis from the liquidcrystal cell 10, and one focal length beyond aperture plate 70 islocated Fourier transform lens 74 which provides an inverse transform.The inverse transform is projected upon output plane 76. This plane maybe a screen for visual observation, a photographic emulsion, anotherliquid crystal sensitive to that wavelength, one or more photodiodes tomeasure the light flux, or a vidicon T.V. pickup. These may be employedeither in the output plane 76 or the transform image plane at processingplane 72. By this means, Fourier transform of the information providedby image 60 and controlled by Fourier processing at plane 72 isaccomplished.

Referring to FIG. 3, the liquid crystal optical processor 80 is verysimilar to the optical processor 50. Laser 82, spatial filter 84, lens86, and chopper 88 are positioned along the optical axis of processor 80and respectively correspond to the equivalent parts described withrespect to processor 50. Similarly, processor 80 contains a liquidcrystal cell 10' which is addressed by incoherently ultravioletlyilluminated image 90 for ZnS photoconductor or blue-green for CdSphotoconductor through shutter 92, lens 94, and beam splitter 96,similarly to the corresponding elements described with respect tooptical processor 50.

First Fourier transform lens 98 is positioned one focal lengthdownstream along the axis from the active part of the liquid crystalcell 10. Furthermore, aperture plate 100 is positioned another focallength downstream along the axis. The aperture plate 100 is at the focalpoint of the collimated light from first'transform lens 98 and, directlyadjacent thereto, is the Fourier processing plane. At the Fourierprocessing plane in optical processor 80 is positioned liquid crystalcell 102. Liquid crystal cell W2 is identical to cell ill) and isactuated in the same way.

As previously described, Fourier processing is accomplished at theprocessing plane by filtration. Optical filtration is accomplished byobstructing transmission of coherent light through certain areas, suchas is accomplished by a transparency. Since the liquid crystal cell 102can be controlled in the same way to provide nontransparent areas,Fourier processing at the processing plane can be accomplished by such aliquid crystal cell. The advantage of the cell is that rapid address isaccomplished so that processing can be varied continuously. Of course,this is true also of the cells with a time varying input thereto.Similarly to the cell 10, liquid crystal cell 102 has an input fromimage 104 which is incoherently illuminated, and its image is projectedthrough shutter 106, lens 108, and beam splitter 110 onto the cell 102to control the transparency of the cell.

The resultant processed image is retransformed by second Fouriertransform lens 112 to appear at output plane 114. It will be recognizedthat the processor 80 is identical to the processor 50, but with thefurther addition of the liquid crystal cell as the Fourier transformprocessor. Thus, both the image input and the processor image can berapidly changed and can include continuously variable inputs andoutputs.

This invention having been described in its preferred embodiment, it isclear that it is susceptible to numerous modifications and embodimentswithin the ability of those skilled in the art.

What is claimed is:

1. An optical processor having an optical axis comprising:

a source of collimated illumination for directing a collimated beam oflight along said axis;

an illumination chopper positioned on said axis for cyclically choppingillumination passing along said axis;

a filter positioned on said axis beyond said chopper and extending atleast partially transversely to said axis for controlling thetransmission of lateral portions of the beam of light in a directionparallel to said axis to produce a laterally patterned light beam, saidfilter comprising a liquid crystal filter;

second illumination means for illuminating an image and projection meansfor projecting said illuminated image onto said liquid crystal filter,said second illumination means being separate from said source ofcollimated illumination, so that said liquid filter can be addressed by'said illuminated .image to produce the laterally patterned light beam;

a lens positioned along said axis downstream from said filter foreffecting a transform of the image in the beam produced by thetransmissivity configuration of said filter, the transform occurring ata transform plane adjacent the focal point of said lens.

2. The optical processor of claim 1 wherein said filter is sensitive toillumination by light having a wavelength in a second range, and saidsecond illumination means illuminates said filter with said image withlight having a wavelength in said second range, and said collimatedsource of illumination for directing light along said axis has awavelength in a first range substantially outside of said second range.

3. The optical processor of claim 2 wherein said liquid crystal filtercomprises first and second spaced filter cover plates, each carrying asubstantially transparent.electric conductive layer, a photoconductor between said filter plate and adjacent one of said cover plates, and aliquid crystal between said photoconductor and the other of said coverplates, so that application of voltage between said electricallyconductive layers applies an electric field across said photoconductorand said liquid crystal.

4. The optical processor of claim 3 wherein said photoconductor in saidliquid crystal filter has reduced resistivity when illuminated by lightof wavelength in said second range so that a portion of the liquidcrystal adjacent the illuminated photoconductor has a higher electricfield applied thereto.

5. The optical processor of claim 4 wherein said liquid crystal is anematic liquid crystal.

6. The optical processor of claim 5 wherein a direct current electricfield with a superimposed alternating current electric field is appliedacross said electrically conductive layer.

7. The optical processor of claim 4 wherein said liquid crystal is aliquid crystal of mixed nematic and cholesteric liquid crystalmaterials.

8. The optical processor of claim 7 wherein a source of direct currentelectrical potential is applied to said electrically conductive layers.

9. The optical processor of claim 1 further including a spatial filterat said transform plane, a retransform lens downstream from saidtransform plane and means for observing the retransformed image alongthe axis downstream from said retransforrn lens, said spatial filter atsaid transform plane being a second liquid crystal filter.

10. The optical processor of claim 9 further including secondillumination means for illuminating a second image and projection meansfor projecting said second illuminated image onto said spatial filter atsaid transform plane, separately from said laser source of illuminationso that said second liquid filter can be addressed by said secondilluminated image.

11. The optical processor of claim 10 wherein said second liquid crystalfilter comprises first and second spaced filter cover plates, eachcarrying a substantially transparent electric conductive layer, aphotoconductor between said cover plates and adjacent one of said coverplates, and a liquid crystal between said photoconductor and the otherof said cover plates so that application of voltage between saidelectrically conductive layers applies an electric field across saidphotoconductor and said liquid crystal.

12. The optical processor of claim 11 wherein said photoconductor insaid second liquid crystal filter has reduced resistivity whenilluminated by light of wavelength to which it is sensitive so that aportion of the liquid crystal adjacent the illuminated photoconductorhas a higher electric field applied thereto.

13. The tgptical processor of claim 12 wherein said liquid crys in saidsecond liquid crystal filter is a nematic liquid crystal.

14. The optical processor of claim 13 wherein a direct current electricfield with a superimposed altemating current electric field is appliedacross said electrically conductive layer.

15. The optical processor of claim 11 wherein said liquid crystal insaid second liquid crystal filter is a liquid crystal of mixed nematicand cholesteric liquid crystal materials.

16. The optical processor of claim 15 wherein a source of direct currentelectrical potential is applied to said electrically conductive layers.

8 t I k

2. The optical processor of claim 1 wherein said filter is sensitive toillumination by light having a wavelength in a second range, and saidsecond illumination means illuminates said filter with said image withlight having a wavelength in said second range, and said collimatedsource of illumination for directing light along said axis has awavelength in a first range substantially outside of said second range.3. The optical processor of claim 2 wherein said liquid crystal filtercomprises first and second spaced filter cover plates, each carrying asubstantially transparent electric conductive layer, a photoconductorbetween said filter plate and adjacent one of said cover plates, and aliquid crystal between said photoconductor and the other of said coverplates, so that application of voltage between said electricallyconductive layers applies an electric field across said photoconductorand said liquid crystal.
 4. The optical processor of claim 3 whereinsaid photoconductor in said liquid crystal filter has reducedresistivity when illuminated by light of wavelength in said second rangeso that a portion of the liquid crystal adjacent the illuminatedphotoconductor has a higher electric field applied thereto.
 5. Theoptical processor of claim 4 wherein said liquid crystal is a nematicliquid crystal.
 6. The optical processor of claim 5 wherein a directcurrent electric field with a superimposed alternating current electricfield is applied across said electrically conductive layer.
 7. Theoptical processor of claim 4 wherein said liquid crystal is a liquidcrystal of mixed nematic and cholesteric liquid crystal materials. 8.The optical processor of claim 7 wherein a source of direct currentelectrical potential is applied to said electrically conductive layers.9. The optical processor of claim 1 further including a spatial filterat said transform plane, a retransform lens downstream from saidtransform plane and means for observing the retransformed image alongthe axis downstream from said retransform lens, said spatial filter atsaid transform plane being a second liquid crystal filter.
 10. Theoptical processor of claim 9 further including second illumination meansfor illuminating a second image and projection means for projecting saidsecond illuminated image onto said spatial filter at said transformplane, separately from said laser source of illumination so that saidsecond liquid filter can be addressed by said second illuminated image.11. The optical processor of claim 10 wherein said second liquid crystalfilter comprises first and second spaced filter cover plates, eachcarrying a substantially transparent electric conductive layer, aphotoconductor between said cover plates and adjacent one of said coverplates, and a liquid crystal between said photoconductor and the otherof said cover plates so that application of voltage between saidelectrically conductive layers applies an electric field across saidphotoconductor and said liquid crystal.
 12. The optical processor ofclaim 11 wherein said photoconductor in said second liquid crystalfilter has reduced resistivity when illuminated by light of wavelengthto which it is sensitive so that a portion of the liquid crystaladjacent the illuminated photoconductor has a higher electric fieldapplied thereto.
 13. The optical processor of claim 12 wherein saidliquid crystal in said second liquid crystal filter is a nematic liquidcrystal.
 14. The optical processor of claim 13 wherein a direct currentelectric field with a superimposed alternating current electric field isapplied across said electrically conductive layer.
 15. The opticalprocessor of claim 11 wherein said liquid crystal in said second liquidcrystal filter is a liquid crystal of mixed nematic and cholestericliquid crystal materials.
 16. The optical processor of claim 15 whereina source of direct current electrical potential is applied to saidelectrically conductive layers.